Endothelial cells in tumor vessels express angiogenic markers that are not detectable in normal vessels. We have developed an in vivo selection system in which phage capable of homing to tumor angiogenic vasculature are recovered from a phage display peptide library following intravenous administration. Using this strategy, we have isolated several tumor-homing phage. Among those were phage displaying a double cyclic RGD (RGD-4C). We have shown that this peptide bind to alpha v integrins in tumor angiogenic vasculature. Based on our in vivo studies targeting tumors with RGD-4C-phage, we propose that such peptide is suitable for generation of vectors for targeted delivery of genes to angiogenic vasculature and tumor cells in vivo. We hypothesized that combining the favorable biological attributes of eukaryotic and prokaryotic viruses may facilitate systemic gene therapy targeting applications. Here we introduce a chimeric vector consisting of genetic elements from adeno-associated virus (AAV) and M13 bacteriophage. These phage/AAV vectors display peptides designed to target the tumor vasculature and tumor cells. We show that the phage/AAV chimera provides improved gene expression over standard phage vectors and that incorporation of AAV inverted terminal repeats likely protects the chimera from chromatin-induced gene silencing. A single systemic dose of our prototype delivered a suicide gene at sufficient efficiency to cause vascular destruction that resulted in significant tumor growth suppression. Together, our results show that phage/AAV chimeras can effectively mediate gene delivery in vivo. This new class of hybrid viruses may prove superior targeted gene therapy vectors. Our Specific Aims are: (i) to develop efficient phage-based vectors for targeted delivery of genes to angiogenic vasculature and tumor cells, (ii) to evaluate the efficiency of gene expression and angiogenesis inhibition upon targeted delivery of proapoptotic genes. Human tumor xenograft models will be used, (iii) to examine the therapeutic effects of targeted delivery of proapoptotic genes to tumors in combination with radiation therapy. Therapy experiments designed to evaluate inhibition of neovascularization, effects on tumor growth and survival by targeted delivery of functional genes and radiation will be performed. Relevance: The studies outlined in this proposal focus on the use of peptide sequences with selective angiogenic vasculature- and tumor cell-targeting properties. We will seek to validate probes as delivery vehicles in gene targeting approaches. Vector targeting would represent a major advance in the management of cancer.